After each of two years my BMW 520d has shown excess oil in the sump. Is this because attempts to clear the particulate filter have dumped fuel into the sump?

I now recognise that this is probably the wrong car for me as I do too many short trips. However, I do try to get the engine up to temperature as often as possible. What length of trip and at what duration would ensure that I clear the soot from the filter?

I am retired and can drive when and where I wish. I am also committed to keeping the car for a while on a financial basis and enjoy how it performs.